In the present state of the art of introducing particulate additives, such as reclaimed aggregate dust or mineral filler, into asphalt drum mixers, the additives are exposed to a spray of liquid asphalt in the drum mixer in an attempt to coat the additives. However, in many instances, a portion of the additives introduced into the drum mixer via the above method escape coating by the liquid asphalt spray. The uncoated additives that do not combine with the mixing aggregate materials within the drum are carried out of the drum in the exhaust gas stream and re-collected by the emission system. Consequently, the work load on the emission system is increased.
The present state of the art of introducing particulate rubber into asphalt drum mixers is largely undeveloped. One process uses a proprietary blender to mix crumb rubber with liquid asphalt, the mixture is then placed in an agitated storage tank for at least an hour. Prior to this invention, asphalt plants required a great deal of additional equipment to enable them to produce asphalt/rubber paving.
The present invention eliminates these disadvantages by providing a closed, pressurized system for thoroughly coating the additives with liquid asphalt. The additives are injected into a stream of liquid asphalt and become suspended therein producing a slurry. In this state, additives (such as dust) adhere to the mixing asphaltic materials within the drum; thus reducing emissions and providing greater control of the product composition. In addition, the present invention provides a simple addition to an asphalt plant for adding rubber to liquid asphalt.